Information About
the Cisco Nexus 2000 Series Fabric Extender

The
Cisco Nexus 2000 Series
Fabric Extender,
also known as FEX, is a highly scalable and flexible server networking solution
that works with
Cisco Nexus Series
devices to provide high-density, low-cost connectivity for server aggregation.
Scaling across 1-Gigabit Ethernet, 10-Gigabit Ethernet, unified fabric, rack,
and blade server environments, the
Fabric Extender
is designed to simplify data center architecture and operations.

The
Fabric Extender
integrates with its parent switch, which is a
Cisco Nexus Series
device, to allow automatic provisioning and configuration taken from the
settings on the parent device. This integration allows large numbers of servers
and hosts to be supported by using the same feature set as the parent device, including security and
quality-of-service (QoS) configuration parameters,
with a single management domain. The
Fabric Extender
and its parent switch enable a large multipath, loop-free, active-active data
center topology without the use of the Spanning Tree Protocol (STP).

The
Cisco Nexus 2000 Series
Fabric Extender
forwards all traffic to its parent
Cisco Nexus Series
device over 10-Gigabit Ethernet fabric uplinks, which allows all traffic to be
inspected by policies established on the
Cisco Nexus Series
device.

No software is
included with the
Fabric Extender.
The software is automatically downloaded and upgraded from its parent device.

Fabric Extender
Terminology

Some terms used in
this document are as follows:

Fabric
interface—A 10-Gigabit Ethernet uplink port that is designated for connection
from the
Fabric Extender
to its parent switch. A fabric interface cannot be used for any other purpose.
It must be directly connected to the parent switch.

Note

A fabric
interface includes the corresponding interface on the parent switch. This
interface is enabled when you enter the
switchport mode
fex-fabric command.

Port channel
fabric interface—A port channel uplink connection from the
Fabric Extender
to its parent switch. This connection consists of fabric interfaces that are
bundled into a single logical channel.

Host
interface—An Ethernet host interface for connection to a server or host system.

Note

Do not connect
a bridge or switch to a host interface. These interfaces are designed to
provide end host or server connectivity.

Note

On Cisco Nexus 2348TQ and Nexus 2348UPQ FEX, if a port channel
is used to connect a parent switch with a
Fabric Extender
device, the port channels can have maximum of 8 ports.

The Nexus 2348 FEX devices have a total of 6 * 40 Gigabit
Ethernet uplink ports towards the parent switch. If these are used with native
40G uplinks port on a parent switch, then there is no limitation. All 6 ports
can be used in either single homed or dual homed configuration. You can also
use 40 Gigabit Ethernet uplink ports on the N2348
Fabric Extender
device with 10 Gigabit Ethernet ports on the parent switch when used with the
appropriate cabling. A maximum of 8 ports can be added to the port channel
between the parent switch and
Fabric Extender
device. If it is a dual homed setup, VPC to the
Fabric Extender
device, only 4 ports per switch are allowed in the port channel.

Fabric Interface
Features

The
FEX fabric interfaces support static port channels. During the initial
discovery and association process, SFP+ validation and digital optical
monitoring (DOM) are performed as follows:

The FEX
performs a local check on the uplink SFP+ transceiver. If it fails the security
check, the LED flashes but the link is still allowed to come up.

The FEX local
check is bypassed if it is running its backup image.

The parent
switch performs SFP validation again when the fabric interface is brought up.
It keeps the fabric interface down if SFP validation fails.

After an interface
on the parent switch is configured in fex-fabric mode, all other features that
were configured on that port and are not relevant to this mode are deactivated.
If the interface is reconfigured to remove fex-fabric mode, the previous
configurations are reactivated.

For
more information about PFC, see the
Cisco Nexus
7000 Series NX-OS Quality of Service Configuration Guide.

Host Interfaces

Layer 3 Host Interfaces

Beginning with Cisco NX-OS Release 5.2, by default, all host interfaces on a Fabric Extender that are connected to a Cisco Nexus 7000 Series parent switch run in Layer 3 mode.

Note

If you have updated the parent switch to Cisco Nexus Release 5.2, previously configured fabric Extender host interfaces retain their default port mode, Layer 2. You can change these ports to Layer 3 mode with the no switchport command.

The host interfaces also support subinterfaces. You can create up to 63 subinterfaces on a Fabric Extender host interface.

Beginning with Cisco NX-OS Release 6.2, port profiles are supported on the host interfaces of a Fabric Extender.

For information about interfaces, see the Cisco Nexus 7000 Series NX-OS Interfaces Configuration Guide.

All
Fabric Extender
host interfaces run as spanning tree edge ports with BPDU Guard enabled and you
cannot configure them as spanning tree network ports.

You can
connect servers that use active/standby teaming, 802.3ad port channels, or
other host-based link redundancy mechanisms to
Fabric Extender
host interfaces.

Any device
that is running spanning tree connected to a
Fabric Extender
host interface results in that host interface being placed in an error-disabled
state when a BPDU is received.

You can
connect only virtual switches that leverages a link redundancy mechanism not
dependent on spanning tree such as Cisco FlexLink or vPC (with the BPDU Filter
enabled) to a
Fabric Extender
host interface. Because spanning tree is not used to eliminate loops, you
should ensure a loop-free topology below the
Fabric Extender
host interfaces.

Ingress and
egress packet counters are provided on each host interface.

For more
information about BPDU Guard, see
the Cisco Nexus 7000 Series NX-OS Layer 2 Switching Configuration Guide.

Host Interface Port Channels

Layer 3 Host Interface Port Channels

The Fabric Extender (FEX) supports host interface port channel configurations. You can combine up to 8 interfaces in a standard mode port channel and 16 interfaces when configured with the Link Aggregation Control Protocol (LACP).

Note

Port channel resources are allocated when the port channel has one or more members.

All members of the port channel must be FEX host interfaces and all host interfaces must be from the same FEX. You cannot mix interfaces from the FEX and the parent switch.

Layer 3 mode is supported on host interface port channels.

A host interface port channel also supports subinterfaces. You can create up to 1000 subinterfaces on a FEX host interface port channel.

For more information about port channels, see the Cisco Nexus 7000 Series NX-OS Interfaces Configuration Guide.

Layer 2 Host Interface Port Channels

The Fabric Extender supports host interface port channel configurations. You can combine up to 8 interfaces in a standard mode port channel and 16 interfaces when configured with the Link Aggregation Control Protocol (LACP).

Note

Port channel resources are allocated when the port channel has one or more members.

All members of the port channel must be Fabric Extender host interfaces and all host interfaces must be from the same Fabric Extender. You cannot mix interfaces from the Fabric Extender and the parent switch.

Layer 2 mode is supported on host interface port channels.

You can configure Layer 2 port channels as access or trunk ports.

Beginning with Cisco NX-OS Release 5.2(1), Fabric Extenders support the host vPC feature where a server can be dual-attached to two different FEXs through a port channel. You must configure parent switches that connect each Fabric Extender (one parent switch per FEX) in a vPC domain.

Minimum Number of Links on a Fabric Port Channel

In a network configuration of dual-homed hosts (active/standby), you can configure the Fabric Extender to support a minimum number of links for fabric port channels (FPCs) with the port-channel min-links command.

When the number of FPC links falls below the specified threshold, the host-facing Cisco Nexus 2000 interfaces are brought down. This process allows for a NIC switchover on the connection between the host and the FEX.

The automatic recovery of Cisco Nexus 2000 Series interfaces to the standby FEX is triggered when the number of FPC links reaches the specified threshold.

Load Balancing Using Host Interface Port Channels

The Cisco NX-OS software allows for load
balancing traffic across all operational interfaces on a FEX host
interface port-channel by hashing the addresses in the frame to a
numerical value that selects one of the links in the channel.
Port-channels provide load balancing by default.

You can configure the type of load-balancing algorithm used. You can choose the load-balancing algorithm that determines which member port to select for egress traffic by looking at the fields in the frame.

You can configure the load-balancing mode to apply to all Fabric Extenders or to specified ones. If load-balancing mode is not configured, Fabric Extenders use the default system configuration. The per-FEX configuration takes precedence over the load-balancing configuration for the entire system. You cannot configure the load-balancing method per port channel.

Note

The default load-balancing mode for Layer 3 interfaces is the source and destination IP address, and the default load-balancing mode for non-IP interfaces is the source and destination MAC address. For more details, see the
Cisco Nexus 7000 Series NX-OS Interfaces
Configuration Guide, Release 6.x.

You can configure the device to use one of the following methods to load balance across the port channel:

Destination MAC address

Source MAC address

Source and destination MAC address

Destination IP address

Source IP address

Source and destination IP address

Source TCP/UDP port number

Destination TCP/UDP port number

Source and destination TCP/UDP port number

Dot1Q VLAN number

Note

You must be in the default virtual device context (VDC) to configure load-balancing method for FEX; if you attempt to configure this feature from another VDC, the system displays an error.

VLANs

For more information about VLANs, see the Cisco Nexus 7000 Series NX-OS Layer 2 Switching Configuration Guide.

Note

The Fabric Extender does not support private VLANs (PVLANs).

Protocol
Offload

To reduce the load
on the control plane of the
Cisco Nexus Series
device,
Cisco NX-OS
allows you to offload link-level protocol processing to the
Fabric Extender
CPU. The following protocols are supported:

Link Layer
Discovery Protocol (LLDP)

Cisco Discovery
Protocol (CDP)

Link Aggregation
Control Protocol (LACP)

Quality of Service

The
Fabric Extender
uses IEEE 802.1p class of service (CoS) values to associate traffic with the
appropriate class. Per-port quality of service (QoS) configuration is
also supported.

Host interfaces support pause frames, which are implemented using IEEE 802.3x
link-level flow control (LLC). By default, flow control send is on and flow
control receive is off on all host interfaces. Autonegotiation is enabled on
the host interfaces. Per-class flow control is set according to the QoS
classes.

For more information about LLC and quality-of-service, see the Cisco Nexus 7000 Series NX-OS Quality of Service Configuration Guide.

Access Control Lists

The
Fabric Extender supports the full range of ingress access control lists (ACLs) that are available on its parent Cisco Nexus Series device.

For more information about ACLs, see the Cisco Nexus 7000 Series NX-OS Security Configuration Guide.

IGMP
Snooping

IGMP snooping is
supported on all host interfaces of the
Fabric Extender.

The
Fabric Extender and its parent switch support
IGMPv2
and
IGMPv3 snooping based only on the destination multicast MAC
address. It does not support snooping that is based on the source MAC address
or on proxy reports.

Switched Port
Analyzer

You can configure
the host interfaces on the
Fabric Extender as Switched Port Analyzer
(SPAN) source ports. You cannot configure
Fabric Extender ports as a SPAN destination.
Only one SPAN session is supported for all the host interfaces on the same
Fabric Extender. Ingress source (Rx), egress
source (Tx), or both ingress and egress monitoring are supported.

Note

All IP multicast
traffic on the VLANs that a
Fabric Extender host interface belongs to is
captured in the SPAN session. You cannot separate the traffic by IP multicast
group membership.

If you configure
ingress monitoring and egress monitoring for host interfaces on the same
Fabric Extender, you might see a packet
twice: once as the packet ingresses on an interface with Rx configured, and
again as the packet egresses on an interface with Tx configured.

For
more information about SPAN, see the
Cisco Nexus
7000 Series NX-OS System Management Configuration Guide.

Oversubscription

In a switching
environment, oversubscription is the practice of connecting multiple devices to
the same interface to optimize port usage. An interface can support a
connection that runs at its maximum speed. Because most interfaces do not run
at their maximum speeds, you can take advantage of unused bandwidth by sharing
ports. Oversubscription, which is a function of the available fabric interfaces
to active host interfaces, provides cost-effective scalability and flexibility
for Ethernet environments.

The
Cisco Nexus 2248TPFabric Extender has 4 10-Gigabit Ethernet fabric
interfaces and 48 100/1000BASE-T (100-Mb/1-Gigabit) Ethernet host interfaces.
When its host interfaces are running in Gigabit Ethernet mode, it offers
the
following configurations:

The
Cisco Nexus 2248PQ Fabric Extender has 16 10-Gigabit Ethernet fabric interfaces
and 48 10-Gigabit Ethernet host interfaces. All host interfaces use all of the
available fabric interfaces.
When all host interfaces are sending traffic to all fabric interfaces,
the maximum oversubscription ratio for the Cisco Nexus 2248PQ is 3:1.

The
Cisco Nexus 2232PPFabric Extender has 8 10-Gigabit Ethernet fabric
interfaces and 32 10-Gigabit Ethernet host interfaces. All host interfaces use
all of the available fabric interfaces. (Static pinning is not supported.
Port-channel mode is supported only on fabric interfaces.) When all host
interfaces are sending traffic to all fabric interfaces, the maximum
oversubscription ratio for the Cisco Nexus 2232PP is 4:1.

The
Cisco Nexus 2232TM and Cisco Nexus 2232TM-E Fabric Extenders have 8 10-Gigabit
Ethernet fabric interfaces and 32 Gigabit and 10-Gigabit Ethernet host
interfaces. All host interfaces use all of the available fabric interfaces.
When all host interfaces are sending traffic to all fabric interfaces,
the maximum oversubscription ratio for the Cisco Nexus 2232TM and Cisco Nexus
2232TM-E is 4:1.

The
Cisco Nexus B22 Fabric Extender for HP (NB22HP) has 8 10-Gigabit Ethernet
fabric interfaces and 16 1G/10-Gigabit Ethernet host interfaces. All host
interfaces use all of the available fabric interfaces.
When all host interfaces are sending traffic to all fabric interfaces,
the maximum oversubscription ratio for the Cisco Nexus B22 Fabric Extender for
HP (N2K-B22HP-P) is 2:1.

Management
Model

The
Cisco Nexus 2000 Series
Fabric Extender is managed by its parent switch over
the fabric interfaces through a zero-touch configuration model. The switch
discovers the
Fabric Extender by detecting the fabric interfaces of
the
Fabric Extender.

After discovery, if
the
Fabric Extender has been correctly associated with the
parent switch, the following operations are performed:

The switch
checks the software image compatibility and upgrades the
Fabric Extender if necessary.

The switch and
Fabric Extender establish in-band IP connectivity with
each other.

The
switch assigns an IP address in the range of loopback addresses (127.15.1.0/24)
to the
Fabric Extender
to avoid conflicts with IP addresses that might be in use on the network.

The switch
pushes the configuration data to the
Fabric Extender. The
Fabric Extender does not store any configuration
locally.

The
Fabric Extender updates the switch with its
operational status. All
Fabric Extender information is displayed using the
switch commands for monitoring and troubleshooting.

Forwarding Model

The
Cisco Nexus 2000 Series
Fabric Extender
does not perform any local switching. All traffic is sent to the parent switch
that provides central forwarding and policy enforcement, including host-to-host
communications between two systems that are connected to the same
Fabric Extender
as shown in the following figure.

Figure 1. Forwarding Model

The forwarding model facilitates feature consistency between the
Fabric Extender
and its parent Cisco Nexus Series device.

Note

The
Fabric Extender
provides end-host connectivity into the network fabric. As a result, BPDU Guard is enabled on all its host interfaces. If you
connect a bridge or switch to a host interface, that interface is placed in an
error-disabled state when a BPDU is received.

You cannot disable BPDU Guard on the host interfaces of the
Fabric Extender.

The
Fabric Extender
supports egress multicast replication from the network to the host. Packets
that are sent from the parent switch for multicast addresses attached to the
Fabric Extender
are replicated by the
Fabric Extender
ASICs and are then sent to corresponding hosts.

Port Channel Fabric Interface Connection

To provide load balancing between the host interfaces and the parent
switch, you can configure the
Fabric Extender
to use a port channel fabric interface connection. This connection bundles
10-Gigabit Ethernet fabric interfaces into a single logical channel as shown in
the following figure.

Figure 2. Port Channel Fabric Interface Connection

When you configure the
Fabric Extender
to use a port channel fabric interface connection to its parent switch, the
switch load balances the traffic from the hosts that are connected to the host
interface ports by using the following load-balancing criteria to select the
link:

For a Layer 2 frame, the switch uses the source and destination
MAC addresses.

For a Layer 3 frame, the switch uses the source and destination
MAC addresses and the source and destination IP addresses.

Note

A fabric interface that fails in the port channel does not trigger a
change to the host interfaces. Traffic is automatically redistributed across
the remaining links in the port channel fabric interface.
If all links in the fabric port channel go down, all host interfaces on the FEX are set to the down state.

Port Numbering
Convention

The following port
numbering convention is used for the
Fabric Extender:

interfaceethernetchassis/slot/port

where

chassis is
configured by the administrator. A
Fabric Extender must be directly connected to its
parent
Cisco Nexus Series device via a port channel fabric
interface. You configure a chassis ID on a port channel on the switch to
identify the
Fabric Extender that is discovered through those
interfaces.

The chassis ID
ranges from
101
to 199.

Note

The chassis
ID is required only to access a host interface on the
Fabric Extender. A value of less than
101
indicates a slot on the parent switch. The following port numbering convention
is used for the interfaces on the switch:

interfaceethernetslot/port

slot
identifies the slot number on the
Fabric Extender.

port
identifies the port number on a specific slot and chassis ID.

Fabric Extender Image Management

No software ships with the
Cisco Nexus 2000 Series
Fabric Extender.
The
Fabric Extender
image is bundled into the system image of the parent switch. The image is
automatically verified and updated (if required) during the association process
between the parent switch and the
Fabric Extender.

When you enter the
install all command, it upgrades the software on the parent
Cisco Nexus Series
switch and also upgrades the software on any attached
Fabric Extender.
To minimize downtime as much as possible, the
Fabric Extender
remains online while the installation process loads its new software image.
Once the software image has successfully loaded, the parent switch and the
Fabric Extender
both automatically reboot.

This process is required to maintain version
compatibility between the parent switch and the
Fabric Extender.

Licensing Requirements for the Fabric Extender

The following table shows the licensing requirements for the Cisco Nexus 2000 Series Fabric Extender:

Product

License Requirement

Cisco NX-OS

The Cisco Nexus 2000 Series Fabric Extender requires no license. Any feature not included in a license package is bundled with the Cisco NX-OS system images and is provided at no extra charge to you. For an explanation of the licensing scheme, see the
Cisco NX-OS Licensing Configuration Guide.

Guidelines and
Limitations for the Fabric Extender

The Cisco Nexus 2000
Series Fabric Extender (FEX) has the following configuration guidelines and
limitations:

You must enable
the Fabric Extender feature set in the default virtual device context (VDC).
After you enable the feature set in the default VDC, the FEX can belong to any
VDC and can be configured from those VDCs.

Each Fabric
Extender that is connected to a chassis must have a unique FEX ID. The same FEX
ID cannot be configured for two or more Fabric Extenders even if the Fabric
Extenders are in separate VDCs.

The FEX ID for a
Fabric Extender is persistent across a chassis. The FEX ID is not reset when
used in a VDC.

All the uplinks
and host ports of a Fabric Extender belong to a single VDC. The ports cannot be
allocated or split among multiple VDCs.

The Fabric
Extender feature set operation might cause the standby supervisor to reload if
it is in an unstable state, such as following a service failure or powering up.
You can check whether the standby supervisor is stable by using the
show modules
command. When the standby supervisor is stable, it is indicated as ha-standby.

You can configure
the Fabric Extender host interfaces as edge ports only. The interface is placed
in an error-disabled state if a downstream switch is detected.

The Fabric
Extender does not support PVLANs.

For Cisco NX-OS
Release 6.2(2) and later releases, the FEX supports queuing, which allows a
router to be connected to a Layer 3 FEX interface or a router to be connected
to a Layer 2 FEX interface (using SVI).

Follow these
guidelines for a router that is connected to a Layer 2 FEX interface (using
SVI):

You can
configure routing adjacency with Layer 3 on the peer router.

You can
configure routing adjacency with SVI on the router using access/trunk
interfaces.

Note

FEX
interfaces do not support the spanning tree protocol.

You must
configure the network without the possibility of any loops.

For Cisco NX-OS
Release 6.2(2) and later releases, the Cisco Fabric Extender supports routing
protocol adjacency. Before Cisco NX-OS Release 6.2(2), the Fabric Extender
cannot participate in a routing protocol adjacency with a device attached to
its port. Only a static direct route is supported. This restriction applies to
both of the following supported connectivity cases:

An SVI with
a FEX single port or portchannel in Layer 2 mode.

A FEX port
or portchannel in Layer 3 mode.

For Cisco NX-OS
Release 6.2(2) and later releases, the Cisco Fabric Extender supports the
following:

Queuing for
Ethernet frames on a FEX-based CoS and DSCP values and support for queuing
Fibre Channel over Ethernet (FCoE) frames on a FEX.

For Cisco NX-OS
Release 6.2(2) and later releases, the Cisco Fabric Extender supports optimized
multicast flooding (OMF) is available on FEX ports.

The Cisco Fabric
Extender does not support policy based routing (PBR).

Beginning with Cisco NX-OS Release 6.2(2), the configured MTU for
the FEX ports is controlled by the network QoS policy. To change the MTU that
is configured on the FEX ports, modify the network QoS policy to change when
the fabric port MTU is also changed.

Associating with F2-Series Modules

Each port in the ASIC has an index. Allow only ports with similar indices across ASICs to be added to a port channel.

For example, if port 1 has an index of 1 and port 2 has an index of 2, the following ports are supported and not supported:

Supported: Port 1 of ASIC 1 and port 1 of ASIC 2 are added to a port channel.

Not supported: Port 1 of ASIC 1 and port 2 of ASIC 2 to form a port channel.

A set of ports from an ASIC that has an index sub-set S, such as {1,2,4}, is allowed to be added to a port channel only if the port channel has an equivalent or an empty set.

FEX Queuing
Support

FEX QoS Queuing Support

Fabric Extenders
(FEXs) follow the network quality of service (QoS) queuing model for supporting
queuing on FEX host interfaces, regardless of whether the FEX is connected to
M-series or F-series fabric uplinks.

Depending on
the network-QoS template that is attached to the system QoS, the following
parameters are inherited for queuing support on a FEX:

Number of
queues

Class of
service (CoS2q) mapping

Differentiated services code point (DSCP2q) mapping

Maximum
transmission unit (MTU)

For both
ingress and egress queuing on the FEX host interfaces, all of the preceding
parameters are derived from the ingress queuing parameters that are defined in
the active network-QoS policy. The egress queuing parameters of the active
network-QoS policy do not affect the FEX host-port queuing.

Such
parameters as the bandwidth, queue limit, priority, and set CoS in the
network-QoS type queuing-policy maps are not supported for a FEX.

Hardware Queue-limit
Support

The following
example shows how to configure the queue limit for a FEX by using the
hardwarefex-type
queue-limit command in the FEX configuration mode:

The value of the
queue limit that is displayed for a FEX interface is 0 bytes until after the
first time the FEX interface is brought up. After the interface comes up, the
output includes the default queue limit or the user-defined queue limit based
on the hardware queue-limit configuration. If the hardware queue limit is
unconfigured, “Queue limit: Disabled” is displayed in the command output. The
following partial output of the
show queuing interfaceinterface command shows the queue limit that is
enforced on a FEX:

The
show queuing interfaceinterface command is supported for FEX host
interfaces. The following sample output of this command for FEX host interfaces
includes the number of queues used, the mapping for each queue, the
corresponding queue MTU, the enforced hardware queue limit, and the ingress and
egress queue statistics.

Note

There is no
support to clear the queuing statistics shown in this output.

In Cisco NX-OS
Release 6.2(2) and later releases, FEX queuing is disabled by default on all
existing FEXs after an in-service software upgrade (ISSU). FEX queuing is
enabled upon flapping the FEX. You can reload the FEX to enable queuing on any
FEX after an ISSU. A message is displayed in the output of the
show queuing interfaceinterface command for the FEX host interface after
an ISSU.

For any new FEXs
brought online after an ISSU, queuing is enabled by default.

The queue limit
is enabled by default for all FEXs, regardless of whether queuing is enabled or
disabled for the FEX. In Cisco NX-OS Release 6.2(2), all FEXs come up with the
default hardware queue-limit value. Any user-defined queue limit that is
configured after an ISSU by using the
hardware queue-limit
command takes effect even if queuing is not enabled
for the FEX.

No Support on the Cisco Nexus
2248PQ 10-Gigabit Ethernet Fabric Extender

The following
sample output shows that FEX queuing is not supported for the Cisco Nexus
2248PQ 10-Gigabit Ethernet Fabric Extender (FEX2248PQ):

For FEXs that
are connected to M-series uplinks, the queuing structure is different on FEX
host interfaces and FEX fabric interfaces. The M series queuing policies must
be consistent with the FEX queuing policies.

MTU

FEX queue MTU
configurations are derived from type network-QoS policy-map templates. MTU
changes are applied on cloned network-QoS policy maps. The MTU that is
configured on a FEX port must match the MTU in the network-QoS policy map so
that the FEX MTU can be applied to the FEX host interfaces.
For more information, see the
Cisco
Nexus 7000 Series NX-OS Quality of Service Configuration Guide.

Note

Starting with Cisco NX-OS Release 6.2(2), the configured MTU
for the FEX ports is controlled by the network QoS policy. To change the MTU
that is configured on the FEX ports, modify the network QoS policy to change
when the fabric port MTU is also changed.

If you change the FEX fabric port MTU on a version prior to
Cisco NX-OS Release 6.2(x), and then upgrade via ISSU to Cisco NX-OS Release
6.2(x) or a later version, you will not get any issues until either a FEX or
switch is reloaded. It is recommended that post-upgrade, the FEX HIF MTU be
changed via the network QoS policy as described above.

Qos policy changes affects only F series cards and M series
cards.

Configuration Limits

The configuration limits are documented in the Cisco Nexus 7000 Series NX-OS Verified Scalability Guide.

Default Settings

This table lists the default settings for the Fabric Extender parameters.